The prior art teaches the production of meta- and para-diisopropylbenzene dihydroperoxide by the liquid phase oxidation of meta- and para-diisopropylbenzene with molecular oxygen in the presence of alkaline materials.
This oxidation reaction yields an oxidate which contains dihydroperoxide, monohydroperoxide, unreacted diisopropylbenzene, (2-hydroperoxy-2-propyl) phenyldimethylcarbinol, and small amounts of other reaction by-products. For this discussion, the (2-hydroperoxy-2-propyl) phenyldimethylcarbinol will be referred to as carbinol hydroperoxide and will be prefaced with p- or m- to indicate the para- or meta- isomer thereof. The proportion of monohydroperoxide relative to dihydroperoxide is large in the oxidate, there typically being 2 to 3 times as much monohydroperoxide as dihydroperoxide. Unreacted diisopropylbenzene is also present in large amounts in the oxidate product when dihydroperoxide is the desired product, since if the oxidation is carried too far toward completion the efficiency of dihydroperoxide production decreases as by-products increase. Therefore, the oxidation is typically carried to 30 to 40% completion based upon all hydroperoxide calculated as dihydroperoxide. The carbinol hydroperoxide is a by-product of the oxidation reaction and typically exists in an amount equal to about 20% of the dihydroperoxide present in the oxidate. The other oxidation by-products are present in small amounts, typically amounting to a few percent of the total oxidate.
The dihydroperoxide, when it is the desired product, has heretofore been recovered from the oxidate by extraction techniques, for example, with dilute aqueous solutions of alkali metal hydroxides of from about 1 to about 15% concentrations. Although the dihydroperoxide is extracted from most of the oxidate materials by the use of dilute aqueous alkali metal hydroxide solutions, the dihydroperoxide is not separated from the carbinol hydroperoxide. If it is required to recover the dihydroperoxide in substantial purity, then further measures must be taken to separate it from the carbinol hydroperoxide, for instance by further extraction from an organic solution with concentrated solutions of alkali metal hydroxides as described in U.S. Pat. No. 2,812,357. When the dihydroperoxide is so purified, employing concentrated solutions of alkali metal hydroperoxide, the dihydroperoxide is recovered as a solid alkali metal salt of the dihydroperoxide.
One method of regenerating the dihydroperoxide from its alkali metal salt is be treating a mixture of the salt of the dihydroperoxide in water with a weak acid. The weak acid reacts with the salt to form the dihydroperoxide, which is insoluble in water, and the alkali metal salt of the acid. The dihydroperoxide separates from the water phase and may be conveniently recovered by a physical separation means, such as decantation, filtration, centrifugation, etc. The amount of water present should be sufficient to dissolve the alkali metal salts of the acid which result from the acid treatment. The dihydroperoxide recovered by this method will be wet with the water solution of the salt. Any residual amount of the salt may be conveniently removed from the dihydroperoxide by washing the dihydroperoxide with water or with other wash materials in which the dihydroperoxide is relatively insoluble.
Any weakly acidic material may be used in this method of recovering dihydroperoxide from its alkali metal salt. The acids which may be employed include CO.sub.2, acetic acid, other carboxylic acids, and dilute mineral acids. The preferred acid is CO.sub.2 as it does not react to degrade the dihydroperoxide and is economical to use. The stronger acids, particularly the mineral acids, will react with the dihydroperoxides and destroy them unless the acids are carefully diluted. Such a reaction by the acid will decrease the dihydroperoxide yield and purity.
Another method of recovering the dialkylbenzene dihydroperoxide from its alkali metal salt is to dissolve the alkali metal salt in water to form a dilute aqueous solution. This aqueous solution is treated in an extraction process with a water-insoluble extraction liquid selected from the group comprising aliphatic ketones, aliphatic ethers, aliphatic alcohols and chlorinated aliphatic hydrocarbons, at a temperature of from 70.degree. to 100.degree. C. and in a ratio of extraction component to alkali phase of 0.2-5:1 and thereby extract the dihydroperoxide from the aqueous alkali phase. The dihydroperoxide may be recovered free of the organic solvent by vaporizing such solvent, thus yielding a crystalline hydroperoxide product. This method of recovering dialkylbenzene dihydroperoxide from its alkali metal salt is described in more detail in U.S. Pat. No. 3,190,923.
The dihydroperoxide, on recovery from the oxidate, is useful in the production of dihydric phenols and carbonyl compounds. For instance, the para-diisopropylbenzene dihydroperoxide can be rearranged, in the presence of an acid catalyst, to form hydroquinone and acetone, and the meta-diisopropylbenzene dihydroperoxide can be rearranged in the presence of an acid catalyst to form resorcinol and acetone.
From the point of view of producing hydroquinone and resorcinol with a minimum amount of contaminants and side reaction products, it is desirable to provide a substantially pure dihydroperoxide to the rearrangement reaction. For instance, any monohydroperoxide will rearrange to form isopropylphenol, which is a contaminant, and carbinol hydroperoxide will rearrange to form (2-hydroxy-2-propyl) phenol which is a contaminant, and which may dehydrate in the presence of the acid catalyst to form isopropenylphenol and, in either case, will tend to condense with the dihydric phenol to form a side reaction product and thereby reduce the yield of desired dihydric phenols. A dihydroperoxide of substantial purity may be easily recovered from a substantially pure metal salt of dihydroperoxide and its recovery in substantial purity and good yield from an oxidate is a first step toward the production of hydroquinone and resorcinol. The alkali metal salts of the dihydroperoxides are also useful as polymerization initiators for emulsion polymerizations.